Character rigging: Blender keep offset is not working
Here are some things you may have done wrong: 

1- try selecting the bone that you want to be the child FIRST.



2- ofset effect will ONLY work in POSE mode

3- make sure ALL the bones are in the SAME metarig otherwise it won't work as you are trying to do

Wrong way: 
If they are like the ones above, try joining them and repeat the process of parenting

Right way:

I Hope this helps.